Unknown plants...to eat or not to eat??

Growing up in America we were always told, "Never, EVER eat anything in the wild if you are not 100% certain what it is!"  This was beat into us as children.  As a parent I completely agree with repeating this over and over to our girls.  I don't want them to eat a poisonous plant by accident.  I find this is even more important to reiterate here becuase our children see people eat things from the wild often.  One of my friends popped a wild plum into her mouth last summer and before she did she said, "I think these are the wild plums I was told about but don't qoute me on that."  I was shocked that she would just so easily risk eating something if she wasn't sure.  I was reminded again of this practice of trying things today from our neighbor.  I was doing weeding in our garden and there is a plant that is coming up randomly throughout the garden.  It has some pretty large roots.  We were wondering maybe if it was horseradish.  We looked it up online and the leaves looked different but maybe this was another variety.  I brought the plant next door to ask our neighbor.  I had to laugh (to myself) when he took the root and bit into it to taste it.  He chewed on it and spit it out and told me it wasn't.  He then came over to see the other plants and told me definitely no it wasn't horseradish.  He is a very nice neighbor and it is nice to have him around again now that the weather is getting nice (his house is a summer cottage).  The Czech way of eating things in nature still amazes me and I have to laugh at how differently we must have been brought up.